The present invention relates to a structure of a power train system comprising an engine, and electric rotary machine (hereinafter, one primarily used for driving is called an electric motor, one primarily used for generating power and starting an engine is called a power generator and one used for driving and generating power with generally the same frequency of each is called a motor generator) and a gear change mechanism, and more particularly to a power transmission apparatus for improving a transmission efficiency of a power train system.
In view of global environment problems, it becomes important to establish a hybrid control system for motor vehicles, in which a great reduction of specific fuel consumption can be expected.
In JP-A-10-217779, there is disclosed an integrated hybrid power transmission apparatus constituted by a single electric rotary machine, a speed change gear mechanism and a clutch mechanism. The apparatus disclosed in the publication is so constituted that the gear change mechanism, having the electric rotary machine and the clutch mechanism, is integrally contained in a housing of the power transmission apparatus to make the power train system compact and light in weight. Further, by always connecting an input shaft of the gear change mechanism with the electric rotary machine, it is possible to provide a driving manner so-called “series hybrid system” in which an engine drives only the electric rotary machine to generate a power by a part of which other electric rotary machines are driven to run a vehicle. The engine and the electric rotary machine are totally controlled so as to satisfy a feeling of speed acceleration and deceleration desired by a driver and operate the engine and the electric rotary machine in a high efficiency zone.
The system shown in JP-A-10-217779 has the following problems.
First, in order to reduce a torque shock during changing a gear change ratio, for example, from a first speed to a second speed or from a second speed to a third speed, it is necessary to arrange the electric rotary machine at a drive wheel side to the gear change mechanism. On the contrary, in order to generate power by the engine drive force in the series hybrid manner, it is necessary to arrange the electric rotary machine in the engine side to the gear change mechanism. Accordingly, in order to prevent the gear change shock and also improve the gear change performance, at least two or more electric rotary machines are required, resulting in a problem that the drive system becomes a large size.
Second, since a torque transfer mechanism of the engine output shaft to an electric rotary machine output shaft is complex, an efficiency of torque transmission is low.
Third, since the drive system is so constituted that the electric rotary machine is driven by the engine, an inertia torque of the rotor of the electric rotary machine is exerted on the engine side as a load. Thus, during running under the engine drive, in order to correctly execute an acceleration command from the driver, it is necessary to generate an additional torque for canceling the inertia torque in the engine side as well as the torque corresponding to the acceleration command. This poses a problem that the specific fuel consumption is deteriorated in order to improve a driving performance.